It is known from T. Otsuji, Y. M. Meziani, T. Nishimura, T. Suemitsu, W. Knap, E. Sano. T. Asano and V. V. Popov: “Emission of terahertz radiation from dual grating gate plasmon-resonant emitters fabricated with InGaP/InGaAs/GaAs material systems”, J. Phys.: Condens. Matter 20 (2008) 384206, to equip a field effect transistor with a grating-like gate electrode. Adjacent contact surfaces of the grating-like gate electrode are connected to different electric potentials. As a result, plasmons are excited by the flow of electrons flowing in the channel of the field effect transistor. The plasmons have oscillation frequencies between approximately 600 gigahertz and approximately 3 terahertz, and therefore it is possible to excite corresponding electromagnetic waves. This known radiation source has, however, the drawback that the output is merely approximately 1 μW. Yet some technical applications require an output of about 1 mW.
It is known from Shur, M. S.; Lu, J.-Q.; Dyakonov, M. I.: Plasma wave electronics: terahertz sources and detectors using two dimensional electronic fluid in high electron mobility transistors. Terahertz Electronics Proceedings, 1998. THz Ninety Eight. 1998 IEEE Sixth International Conference, pages 127-130, that plasmon oscillations are excited in individual field effect transistors by an electric current between source and drain contacts. The excitation of plasmon oscillations calls for a high mobility of the charge carriers and a ballistic electron transport in the channel. The frequency of the plasmon oscillations excited in the field effect transistors, which is equal to the frequency f of the emitted electromagnetic radiation, has the following relation to the propagation velocity of surface plasmons s and the gate length of the field effect transistors LG
  f  =            s      ·              (                              2            ⁢            k                    -          1                )                    4      ⁢              L        G            wherein k=1, 2, 3, . . . . The propagation velocity s of surface plasmons is at the order of 106 m/s, thus leading to frequencies f of plasmonic waves and the corresponding emitted radiation in the terahertz range with gate lengths ranging from several nanometers to several hundred nanometers. The parameter k here defines the number of plasmonic half-waves which are formed on the gate length of the field effect transistors LG plus 0.5. Therefore, when k=1, plasmon oscillations are produced, the wavelength of which corresponds to four times the gate length LG. When k=2, ¾ wavelengths of the plasmon oscillation are produced over the gate length LG.
Proceeding from the prior art, the object of the invention is therefore to provide a radiation source for far infrared and/or terahertz radiation, which has a greater output.
This object is achieved by a radiation source according to claim 1 and a method according to claim 16.